Peroxidation process



United States Patent 7 PEROXIDATION PROCESS David R. Stern, Fullerton, and Joseph C. Schumacher, Los Angeles, Calif., assignors to American Potash & Chemical Corporation, a corporation of Delaware No Drawing. Application May 6, 1957 Serial No. 657,021

7 Claims. (Cl. 204-432) This invention relates to electrolytic peroxidation processes which require platinum anodes such as the production of perchloric acid, perchlorates, persulfates, periodates, perborates, perbromates,-and various organic oxidations such as the preparation of anthraquinone, and para-aminophenol. The invention will be particularly set forth as it has been applied to the production of sodium perchlorate, but itis not'limited to this.

Sodium perchlorate is one of the starting raw materials for the production of ammonium perchlorate which is used for the manufacture of jet assisted take off units and other rocket applications. However, the large scale use of ammonium perchlorate has been limited by the method of manufacture of sodium perchlorate.

Perchlorates have been customarily produced by electrolysis of sodium chlorate solution utilizing aplatinum anode and a steel cathode. The high cost of platinum, its unavailability, and the fact that it erodes away in use and cannot be recovered has resulted in a process with substantial limitations. Moreover, to utilize steel as a cathode and cell material it has been necessary to add chromates or dichromates as inhibitors. These inhibitors are frequently. carried over intothe end product as a contaminant which is diflicult to remove, and which makes the end product less desirable.

Production of perchlorates by electrolysis using a lead dioxide anode in various geometric shapes along with a solid nickel or a stainless steel cathode has been proposed by a number of investigators. This substitution of solid nickel or stainless steel has been an improvement; nevertheless, there stillremains the disadvantage that solid nickel and stainless steel are expensive, and are difficult to fabricate into large commercial cells. Furthermore, existing steel cells used in commercial production, representing a considerable investment, cannot be converted to use with lead dioxide anodes. Moreover, many investigators, who have proposed nickel and stainless steel as cathode materials with lead dioxide anodes, have concluded that they were unsatisfactory. These prior art processes have in truth been misleading for they have, in some instances, either deliberatelyor unintentionally added dichromates as impurities to their electrolyte. In most chlorate processes the chromate is added as an inhibitor and appears as an impurity in the feed to the perchlorate cells. If the anode in this cell is of platinum and the cathode is steel, the dichromate is beneficial. However, we have found that dichromate is detrimental to a process using a lead dioxide anode and either nickel or stainless steel as a cathode.

We have discovered that chemically-plated nickel-onsteel as a cathode material in conjunction with lead dioxide as an anode can be used advantageously to convert sodium chlorate to sodium perchlorate. Using these electrodes, we have been able to convert chlorates to perchlorates at cumulative current efiiciencies equal to those obtained with platinum and steel electrodes. Also,

the energy requirement for cells made in accordance with 2. our invention is lower than that for the platinum-steel combination. A further advantage is that with the chemically-plated nickel-on-steel' cathode, it is not necessary to control the pH of the electrolyte, since the pH appears to reach anequilibrium in the desirable range of In contrast, present commercial practice with platinum-steel electrodes requires-the'continued addition of acid to maintain the pH on the acid side. Still another advantage of our process was discovered in the course of our investigation when chemically-plated-nickel was compared with electrolytically-plated'nickel, for we found that the corrosion resistance of chemically-plated nickel to the cell solution is greater than that of electrolytically-plated nickel. Finally, electrolytically-plated nickel cannot be applied easily to complicated'shapes required for commercial cells because some type of metal flashing must be effected prior to electrolytically depositing the nickel plate.

The actual chemical plating of nickel on steel'or other metals is well known in the art and constitutes no part of this invention herein described and claimed. Instead of steel onecan use any other metal consistent with the electrolyte and the conditions of use such as copper and aluminum;

We have also discovered that the addition of' sodium fluoride or other alkali metal fluoride increases thecumulative current efiiciency when incorporated into an electrolyte which is electrolyzed with a lead dioxide anode and chemically-platednickel-on-steel as a cathode. An added advantage of the fluoride as an additive is that the required concentration is extremely low and has no detrimental effect on theend product whe n'present as an impurity. The sodium fluoride may be used in a concentration range of 0.5-2.0 g./l.; however, we'do' not wish to be limited thereto, but prefer to use the-lower value of 0.5 g./l. The addition of sodium fluorideincreases the current efiiciency' when compared to the amps/sq. in. is satisfactory, but we prefer a current'den- 'sity of 1.0 amp/sq. in. which appears 'to give the best current efficiency. Cathode current densities from 0.25

to 1.50 amps/sq. injcan beemployed, but we prefer,

but" do not wish to' be limited thereto, 0.5 amp.'/sq.' in. since this also gives the highest cumulative current efliciency. The preferred densitiesare 0.5- amp./sq.- in. on the cathode and simultaneously 1.0 amp/sq. in. on the anode. v 1

The voltage and amperage for cell operation depend to some extent on cell design and electrolyte circulation. The voltage for cell operation is lower for the lead dioxide chemically-plated nickel-on-steel combination than for any known to us. We have found that the electrolysis proceeds in a potential range of 4.755.2 volts. 7

Finally, we have found that the cumulative current efficiency is a function of the sodium chlorate concentration in the cell electrolyte. The economic cut-off point is a function of the end application. If the sodium perchlorate is to be converted to ammonium perchlorate, the chlorate concentration must be low; hence, it is desirable to have high cumulative current efliciency even down to low sodium chlorate concentrations. The lead dioxide-chemi cally-plated nickel on steel combination does this. 7

To illustrate the practice of this invention, in perchlorate production, an electrolyte containing from about 400 to about 700 g./l. of sodium chlorate, which has been free of sodium chromate or dichromate, and containing O-2.0 g./l. of NaF was fed to an electrolytic cell similar in designto that described in the exception that the anode'was a rough-surfaced, rodshaped, lead dioxide electrode,' dia. x14" in length. The cathode consisted of carbonsteel. with a chemicalnickel plate 2 2.5 mils thick. The temperature wa'slmaintained irithe range of 30 45 C., the production proceeding injan etfici ent and smooth"manner;

Cathode current density Although the data are presented for .a batch cell for purposes of illustration,-the actual operation can readily be. carried out on a continuous basis; I

The sodium perchlorate prepared by this method was later converted to ammonium perchlorate of very high purity, meeting the rigorous requirements for rocketry. There was no contamination of nickel or lead in the product., Although sodium perchlorate is used as an example, we do not wish to be limited thereto, since this combination of lead; dioxide anode and chemically-plated nickel cathode can be used in other electrolytic peroxidation processes, as we havementioned.

We l m;

1. In a process for the electrolytic production of sodium perchlorate, the step of passing a current through a sodium chlorate electrolyte between a lead dioxide anode and a cathode consisting essentially ofnickel plated chemically on a metal ba$,, Said electrolyte being substantially freed of sodium chromate and dichromate. 2. In a process for the electrolytic production of sodium perchlorate, the step of passing a current through a sodium chlorate electrolyte between a lead dioxide anode and fa cathode. consisting essentially of nickel plated chemi- 5.- Patent 2,475,157, with 4. and a cathode consisting essentially of nickel plated chemically on a metal base, the metal being selected from the group consisting of steel, copper and aluminum, said electrolyte being substantially, freed of sodium chromate and dichromate.

4. In a process for the electrolytic production of sodium perchlorate, the step ofpassing a current through a sodium chlorate electrolyte between a lead dioxide anode and a cathode consisting essentially of nickel plated chemically on a metal base, the electrolyte also contain ing a small amount of an alkali metal fluoride, said electrolyte being substantially freed of sodium chromate and dichromate.

' 5. In a process for producing sodium perchlorate, the step of passing a current through an electrolyte between a lead dioxide anode and a cathode consisting essentially of nickel chemically plated on a metal base, the electrolyte consisting essentially of from about 400-700 grams per liter of sodium chlorate containing from about 0.5 to about 2.0 grams per liter of an alkali metal fluoride, the anode current density being from about 0.5 to about 1.5 amperes per square inch under a potential of from about 4.75 to about 5.2 volts, said electrolyte being substantially freed of sodium chromate and dichromate.

6. In a process for producing sodium perchlorate, the step of passing a current through an electrolyte between a lead dioxide anode and a cathode consisting essentially of nickel chemically plated on a metal base, the electrolyte consisting essentially of from about 400-700 grams per liter of sodium chlorate, the anode current density being from about 0.5 to about 1.5 amperes per square inch under a potential of from about 4.75 to about 5.2 volts, said electrolyte being substantially freed of sodium chromate and dichromate.

7. In a process for producing sodium perchlorate, the

, step of passing a current through an electrolyte between cally ona steelbase, said electrolyte being substantially freed of. sodium chromate and dichromate.

3. Ina process for the electrolytic production of sodium perchlorate, the step of passing a current through. a sodium, chlorate electrolyte between a lead dioxide anode a lead dioxide anode and a cathode'consisting essentially of nickel chemically plated on a metal base, the electrolyte consisting essentially of from about 400-700 grams per liter of sodium chlorate, the anode current density be- Ehrhardt Oct. 4, 1932 2,512,973 Schumacher June 27, 1950 FOREIGN PATENTS 298,991 Germany Dec. 5, 1919 

7. IN A PROCESS FOR PRODUCING SODIUM PERCHLORATE, THE STEP OF PASSING A CURRENT THROUGH AN ELECTROLYTE BETWEEN A LEAD DIOXIDE ANODE AND A CATHODE CONSISTING ESSENTIALLY OF NICKEL CHEMICALLY PLATED ON A METAL BASE, THE ELECTROLYTE CONSISTING ESSENTIALLY OF FROM ABOUT 400-700 GRAMS PER LITER OF SODIUM CHLORATE, THE ANODE CURRENT DENSITY BEING SUBSTANTIALLY 1.0 AMPERE PER SQUARE INCH AND THE CATHODE CURRENT DENSITY BEING SUBSTANTIALLY 0.5 AMPERE PER SQUARE INCH. 